EXPLORATION 1997 — America Mineral Fields committed to resuscitating Zairian zinc mine

At the Kipushi zinc-copper mine, a few minutes’ drive from Lubumbashi and a short walk from the Zambian border, it is hard not to be reminded of the faded glory of Zaire’s copper belt. For here, a mammoth zinc deposit, with jewelry-box grades and a 50-year history of production, is producing absolutely nothing.

At least not currently.

A new agreement with the Zairian state mining company, Generale des Carrieres et des Mines (Gecamines), gives America Mineral Fields (AMZ-T) the right to carry out, over two years, a feasibility study aimed at bringing the mine back into production. If the study is positive, the agreement allows America Mineral Fields (AMF) to bring the mine back into production for a 50% share in the operation.

Looming in the background is South African mining house Anglo American, which can elect to provide the first US$100 million of capital expenditures on the project to earn half of AMF’s share.

In 1991, Kipushi was second only to Falconbridge’s (FL-T) Kidd Creek mine near Timmins, Ont., as a low-cost zinc producer: at the time, the metals think-tank CRU estimated Kipushi’s cash cost at US16 cents per lb. The mine is being kept closed while Gecamines concentrates its limited resources on high-margin cobalt production at other centres.

Kipushi, which was known as the Prince Leopold mine during the Belgian colonial period, entered production in 1926 and rapidly became a major zinc producer. It fell on hard times in the early 1990s, as the economic crisis in Zaire robbed Gecamines of its ability to purchase new equipment and maintain the machinery it had. Says AMF director Richard Garnett, “If you think about the life cycle of most mining equipment, it’s about four years.” A development program was under way when Gecamines suspended operations.

Shaft-sinking was within 29 metres of its goal (1,515 metres) and ramp development was down to 1,330 metres. Since then, Gecamines has kept the mine pumped out and has maintained the ventilation and the surface works. A new pumping station, with considerable excess capacity, was commissioned last year.

Kipushi still has an excellent resource base. Gecamines’ latest figures show that down to 1,300 metres (the limit of development), the proven reserve is 6.2 million tonnes grading 14.68% zinc and 2.81% copper. Probable reserves, essentially 1,300-1,500 metres deep, stand at 10.7 million tonnes of 20.05% zinc and 2.04% copper. Extending below that, to 1,800 metres, lies a potential 10.6 million tonnes with an average zinc grade of 21.26% and an average copper grade of 1.67%.

The Kipushi deposit is an immense crosscutting vein (not a massive sulphide), which occupies a faulted contact between carbonates and a sandstone. Kipushi is unique in the copper belt, where no other deposit has a significant quantity of zinc, but its copper (and significant cobalt byproduct) suggest that the deposit is not wholly unrelated to the others. The copper ore minerals are chalcopyrite and bornite, with minor supergene sulphides. Zinc is held in sphalerite, and there is sufficient pyrite that the operation once produced a pyrite concentrate for sulphuric acid.

Sub-level caving

The vein itself is remarkably consistent, always some 50-100 metres wide and with a dip near 60. This reliable size and shape, as well as the competent wall rocks, have allowed decades of exploitation by sub-level caving. Since the grade was so high, dilution had not been a major concern. Consideration of other methods that might limit dilution, such as longhole stoping, will be part of the feasibility study.

In happier times, Kipushi was the site of Gecamines’ zinc concentrator, a facility built in 1935 by Union Miniere du Haut-Katanga, the Belgian mining company that opened up the copper belt in the early years of this century.

Without feed, it is simply mothballed, and could require upgrading. But with the increase in zinc grade at deeper levels of the Kipushi orebody, it may be possible to smelt the ore directly — ore grades are approaching 20%, the same grade the concentrator used to produce.

A zinc and copper smelter at Kipushi could offer a good route back to production. With a number of projects in the copper belt looking at the possibility of production from leachable ores, the sulphuric acid produced by the smelter could have an instant market.

The tailings at Kipushi, too, could become a resource for AMF. About 25 million tonnes of tailings exist, with 2.25% zinc, 0.36% copper, and 1.62% lead — a metal that occurs in abundance at Kipushi but was never recovered in the metallurgical circuits.

The agreement between AMF and Gecamines also includes a regional exploration joint venture around the Kipushi mine, covering a 8,500-sq.-km area that has seen only limited use of modern exploration tools. AMF has also lined up an exploration licence across the border in Zambia, covering the extension of the geology into Zambia.